Electromagnetic wave-elastic wave transducer and method

ABSTRACT

This disclosure is concerned with converting electromagneticwaves to elastic waves (and vice-versa) in successive regions near an end of a magneto-elastic medium wherein electromagnetic energy tunneling is first forced, spin-wave conversion is then achieved, and finally spin wave-elastic wave conversion is effected such that the elastic waves are propagated in the medium (and vice-versa).

.7 United States Patent 1 1 1111 3,753,163

Morgenthaler Aug. 14, 1973 [54] ELECTROMAGNETIC w v s 3,668,568 6/1972 Morgenthaler 333/30 3,530,302 9/1970 Morgenthaler 333/30 X WAVE TRANSDUCER AND METHOD 3,249,882 3/1966 Stem 333/30 Inventor: Frederic Morgenthaler, 3,353,118 11/1967 Olson 333/30 x Wellesley Hills, Mass. 173] Assignee: Chu Associates Inc., Littleton, Primary Examiner-Rud0lph Rolinec Mass Assistant Examiner--Saxfield Chatmon, Jr.

'AttorneyRines and Rines [22] Filed: Dec. 27, 1971 [2!] Appl. No.: 211,976 [57] ABSTRACT This disclosure is concerned with converting electro- [52] U.S. Cl. 333/30 R, 333/30 M, 330/4.6 magnetic-waves to elastic waves (and vice-versa) in [51 Int. Cl. H03h 7/30 successive regions near an end of a magneto-elastic me- [58] Field of Search 333/30, 30 A; dium wherein electromagnetic energy tunneling is first 330/4.6 forced, spin-wave conversion is then achieved, and Finally spin wave-elastic wave conversion is effected such [56] References Cited that the elastic waves are propagated in the medium UNITED STATES PATENTS (and vice-Wm)- 3,309,628 3/1967 Olson 333/30 9 Claims, 1 Drawing Figure 3,444,484 3/1969 Bierig 333/30 r r" 1 1 1 I R R 1 R 1 3 (Ei/Vl (SW) '(ELW) (ELWll (SWll (EWl 1 Tunnel rurjieiT Patented Aug. 14, 1973 .l! .illlllllll (ELW) ELECTROMAGNETIC WAVE-ELASTIC WAVE TRANSDUCER AND METHOD The present invention relates to electromagnetic wave-elastic wave transducers and methods, being particularly directed to such devices involving magnetoelastic media, such as YIG crystals and the like.

The art is replete with numerous types of transducers of this character, as described, for example, at IEEE Transactions on Microwave Theory and Techniques, November, 1969, Vol. MTT-l7, No. 11, pages 927-941. The frequency and power limitations imposed by physical transducer structures, dimensions and constructions, such as piezoelectric CdS, ZnO and similar devices, have, however, seriously limited the applications of such structures. It is to extending the operating frequency range, power and applications of these types of apparatus that the present invention is accordingly directed.

An object of the invention, thus, is to provide a new and improved method of transducing and an improved transducer structure, particularly adapted for YIG and similar magneto-elastic structures, that enables use with extremely high X-band microwave frequencies and increased powers.

A further object is to provide a novel transducer of more general utility, as well.

Other and further objects will be explained hereinafter and are more particularly pointed out in the ap pended claims. In summary, however, the invention, in one of its aspects, involves the provision of tunneling spin-wave conversion (electromagnetic-to-spin wave energy) and spin wave-toelastic wave conversion in successive transduction layers near an end of a magneto-elastic medium. Preferred constructional details are hereinafter discussed.

The invention will now be described with reference to the accompanying drawing, the single FIGURE of which is a greatly magnified side elevation of a preferred construction embodying the invention, with operational wave forms illustrated thereupon to describe the performance.

Referring to the drawing, a YIG or similar magnetoelastic medium, including Ga-doped YIG, Mn-doped YIG, Mn-Ga-doped YIG, Eu-doped YIG, Li-ferrite, as illustrations, is shown at 2, provided at its opposite ends with similar terminal transducing structures 1 and 1', respectively connected with electromagnetic-wave energy conductors, illustrated and described herein generically as antenna or probe structures 3 and 3 for the input and output transmission of electromagnetic currents. In accordance with the invention, a steeply decreasing magnetic field profile A is set up through the transducer layer 1, leveling off through the medium 2 at B, and steeply rising at the other transducer end 1', as shown at C. In practice, the transducing regions I, and I and the regions A and C will, as later explained, preferably be very thin terminal layers of the relatively long medium 2, enabling high frequency and high power operation. The antennas at 3 and 3' may be thin wires or thin deposited strips or conductors.

In accordance with the invention, it has been found that a novel transducing operation can be achieved by appropriate orientation and value of a bias magnetic field H applied axially along the medium 2, in this example, to intersect the steeply decreasing and steeply rising magnetic field profile end characteristics A and C at intermediate points P and P, respectively. Considering the left-hand transducer 1, for example (since the other conversion operation at l is the same, but vice versa), the region R represents the layer where the region l of the steeply decreasing or falling profile portion .A applies; and successive adjacent regions R and R correspond to regions [I and III of the field profile portion A. Under the conditions of operation of the invention, the value of H is selected so as to achieve cut off of the electromagnetic wave input at 3 over the region R,, and suppression of any possible conversion of the electromagnetic energy to spin waves therein. This forces the spin electromagnetic energy applied to R to tunnel through the region R,, as schematically illustrated at EW, until the point P of the profile A is reached at which the tunneled electromagnetic energy becomes converted into spin waves (SW); i.e., at region P of strip R The wavelength of the spin waves (SW) will decrease with decreasing amplitude as they are propagated through the region R as shown, under the decreasing field characteristic II of the magnetic field profile portion A, until the point P" of the medium is reached at which the wavelength is sufficiently decreased to effect splitting conversion from spin waves (SW) to elastic waves (ELW), which are then propagated through the next adjacent region R (where the magnetization profile portion Ill applies), and thence into and through the medium 2.

By this technique, novel transduction is achieved that, because the layer 1 (R,, R R can be made very thin, provides the improved performance of the invention. To achieve the operation above-described, the successive regions R R and R, should have successively increasing saturation magnetization. This may be effected, for example, by growing epitaxial YIG layers at this end of the YIG medium 2 (and at the other end 1 introducing successively increasing amounts of, for example, gallium doping to replace progressively more iron in the YIG. Such doping, while not previously effected for these purposes, may be accomplished, for example, by techniques such as described in Magnetic Effects of Indium and Gallium Substitutions in Yttrium Iron Garnet", Anderson et al., Journal of the Physical Society of Japan, Vol. 17, Supplement B-l, Proceedings of the Conference on Magnetism and Crystallography, September, 1961, and in my earlier US. Pat. No. 3,609,596. Other techniques for producing adjacent crystal layers of successively greater saturation magnetization adjacent the medium 2 may also be employed, including polycrystal ferrite or iron layers adjacent an contacting a single YIG crystal 2.

The epitaxial growth technique for forming the layers may be carried out in serveral ways including chemical vapor deposition and molten dipping. In connection with the former, yttrium chloride, iron chloride andthe like have been mixed within a quartz tube furnace and vapor-deposited at high temperature on a Gd-Ga garnet substrate to produce the desired depositions. In the case of the latter technique, the chemical constituents are prepared in molten form and the substrate is suecessively dipped therein to build up the layers.

The phenomenon underlying the invention has been experimentally verifiedin connection with a YIG crystal 2 about 1 centimeter long and 3mm in diameter cut along the axis. Profiles of the type shown at ABC, though with somewhat less steep terminalfalling and rising portions, have been successfully produced with such a crystal using terminal regions of iron and on poly-crystalline ferrite having a saturation magnetization of about 4,000 gauss, as compared with the saturation magnetization of the YlG medium 2 of about l,750 gauss. Fine wire antennas 3 and 3' were employed constituting extensions of the inner conductors of coaxial lines connecting with the appropriate generating and receiving apparatus. With the applied magnetic field l-l oriented substantially parallel to the longitudinal axis of the medium 2, and varied in value up to about 4000 gauss, time-successive tunneling, spinwave and elastic-wave phenomena were produced providing overall insertion losses of the order of 65 db and delayed outputs of the order of 2 microseconds.

Further modifications will also occur to those skilled in this art, and all such are considered to fall within the spirit and scope of the invention as delineated in the appended claims.

What is claimed is:

l. A method of transducing electromagnetic waves into elastic waves and vice versa, that comprises, producing a magnetic field profile along a magneto-elasticwave supporting medium that steeply decreases at one end and increases at the other end; contacting electromagnetic wave antennae to the said ends of the medium; applying a bias magnetic field to the medium and adjusting the value and orientation thereof to cause its magnetic field operating-level line to intersect the steeply decreasing and increasing portions of the magnetic field profile at intermediate points of such portions such that, as the electromagnetic wave launches into the medium at said one end, it initially encounters in a first region preceding the said intermediate point, both electromagnetic-wave-cutoff and spin wave-conversion-suppression, forcing tunneling through said first region to the next adjacent region at which conversion to spin waves of successively decreasing wavelength occurs, which, in turn, are propagated to a further adjacent region of said steeply decreasing profile portion at which the wavelength has become sufficiently small to effect conversion from spin-wave to elastic-wave energy; and propagating the elastic wave energy into the medium; with the reverse conversion operation occuring at the said other end in the steeply rising magnetic field profile portion.

2. A method of transducing between electromagnetic waves and elastic waves, that comprises, producing a steeply changing magnetic field profile at an end of a magneto-elastic-wave supporting medium; contacting an electro-magnetic wave antenna to said end of the medium; applying a bias magnetic field to the medium of such direction and valve that its magnetic field operating-level line intersects the steeply changing profile at an intermediate point thereof defining a first region thereof, where electromagnetic wave energy is cutoff and spin-wave conversion thereof is suppressed to force tunneling through said first region, with conversion to spin waves of successively changing wavelength occuring along the next adjacent region of the steeply changing profile up to the point where such wavelength is sufficiently small to effect conversion between spin wave and elastic wave energy; the elastic wave energy being supported in the medium adjacent the said end.

3. A method as claimed in claim 2 and in which said bias field is varied to tune the operating frequency of the transducer to predtermined values.

4. An electromagnetic wave-elastic wave transducer having, in combination, a magneto-elastic-wave supporting medium provided at one end with an electromagnetic wave antenna, means for establishing at said one end a magnetic field profile that steeply changes over a narrow portion of the medium near said one end, means for applying a bias magnetic field to the medium of such direction and value that its magnetic field operating-level line intersects the steeply changing profile at an intermediate point defining a first region thereof followed by second and third adjacent regions of the steeply changing profile, the field being adjusted to produce spin electromagnetic-wave cutoff and spin wave conversion suppression along the said first region to force tunneling therealong, with conversion to spin waves of successively changing wavelength along the said second region and with the third region disposed where such wavelength is sufficiently small to effect conversion between spin wave and elastic wave energy; the medium adjacent said one end supporting the elastic wave energy therein.

5. An electromagnetic wave-elastic wave transducer as claimed in claim 4 and in which a second transducer combination as claimed in claim 4 is applied at the other end of the medium to effect reverse conversion between electromagnetic and elastic wave energy thereat.

6. An electromagnetic wave-elastic wave transducer as claimed in claim 4 and in which the said first, second and third regions near said one end thereof comprise successive sections of successively different saturation magnetization to effect such steeply changing magnetic profile characteristics.

7. An electromagnetic wave-elastic wave transducer as claimed in claim 4 and in which said medium comprises YlG material, and the said first, second and third regions near said one end thereof comprise successively varying saturation magnetization epitaxial YIG layers grown upon said one end.

8. An electromagnetic wave-elastic wave transducer as claimed in claim 4 and in which means is provided for controlling the bias magnetic field to tune the transducer to predetermined operating frequencies.

9. An electromagnetic wave-elastic wave transducer as claimed in claim 4 and in which the means provided to produce said steeply changing magnetic profile comprises a further medium disposed adjacent the firstnamed medium but of different saturation magnetizat a t a a 

1. A method of transducing electromagnetic waves into elastic waves and vice versa, that comprises, producing a magnetic field profile along a magneto-elastic-wave supporting medium that steeply decreases at one end and increases at the other end; contacting electromagnetic wave antennae to the said ends of the medium; applying a bias magnetic field to the medium and adjusting the value and orientation thereof to cause its magnetic field operating-level line to intersect the steeply decreasing and increasing portions of the magnetic field profile at intermediate points of such portions such that, as the electromagnetic wave launches into the medium at said one end, it initially encounters in a first region preceding the said intermediate point, both electromagnetic-wave-cutoff and spin wave-conversion-suppression, forcing tunneling through said first region to the next adjacent region at which conversion to spin waves of successively decreasing wavelength occurs, which, in turn, are propagated to a further adjacent region of said steeply decreasing profile portion at which the wavelength has become sufficiently small to effect conversion from spin-wave to elastic-wave energy; and propagating the elastic wave energy into the medium; with the reverse conversion operation occuring at the said other end in the steeply rising magnetic field profile portion.
 2. A method of transducing between electromagnetic waves and elastic waves, that comprises, producing a steeply changing magnetic field profile at an end of a magneto-elastic-wave supporting medium; contacting an electro-magnetic wave antenna to said end of the medium; applying a bias magnetic field to the medium of such direction and valve that its magnetic field operating-level line intersects the steeply changing profile at an intermediate point thereof defining a first region thereof, where electromagnetic wave energy is cutoff and spin-wave conversion thereof is suppressed to force tunneling through said first region, with conversion to spin waves of successively changing wavelength occuring along the next adjacent region of the steeply changing profile up to the point where such wavelength is sufficiently small to effect conversion between spin wave and elastic wave energy; the elastic wave energy being supported in the medium adjacent the said end.
 3. A method as claimed in claim 2 and in which said bias field is varied to tune the operating frequency of the transducer to predtermined values.
 4. An electromagnetic wave-elastic wave transducer having, in combination, a magneto-elastic-wave supporting medium provided at one end with an electromagnetic wave antenna, means for establishing at said one end a magnetic field profile that steeply changes over a narrow portion of the medium near said one end, means for applying a bias magnetic field to thE medium of such direction and value that its magnetic field operating-level line intersects the steeply changing profile at an intermediate point defining a first region thereof followed by second and third adjacent regions of the steeply changing profile, the field being adjusted to produce spin electromagnetic-wave cutoff and spin wave conversion suppression along the said first region to force tunneling therealong, with conversion to spin waves of successively changing wavelength along the said second region and with the third region disposed where such wavelength is sufficiently small to effect conversion between spin wave and elastic wave energy; the medium adjacent said one end supporting the elastic wave energy therein.
 5. An electromagnetic wave-elastic wave transducer as claimed in claim 4 and in which a second transducer combination as claimed in claim 4 is applied at the other end of the medium to effect reverse conversion between electromagnetic and elastic wave energy thereat.
 6. An electromagnetic wave-elastic wave transducer as claimed in claim 4 and in which the said first, second and third regions near said one end thereof comprise successive sections of successively different saturation magnetization to effect such steeply changing magnetic profile characteristics.
 7. An electromagnetic wave-elastic wave transducer as claimed in claim 4 and in which said medium comprises YIG material, and the said first, second and third regions near said one end thereof comprise successively varying saturation magnetization epitaxial YIG layers grown upon said one end.
 8. An electromagnetic wave-elastic wave transducer as claimed in claim 4 and in which means is provided for controlling the bias magnetic field to tune the transducer to predetermined operating frequencies.
 9. An electromagnetic wave-elastic wave transducer as claimed in claim 4 and in which the means provided to produce said steeply changing magnetic profile comprises a further medium disposed adjacent the first-named medium but of different saturation magnetization. 